The present invention relates to a tensioning device (also referred to as a “belt tightener”) for an occupant restraint such as a seat belt and/or shoulder harness.
A typical occupant restraint system for a vehicle comprises a belt system anchored to structural parts of the vehicle such as the floor, a pillar such as a B pillar or to a seat frame. Where the restraint system includes a shoulder harness, the shoulder harness typically extends through a web guide that is coupled to a structural part of the vehicle such as the B pillar or the seat frame. A retractor, often called an “ELR or emergency locking retractor,” is part of the restraint system. The retractor allows payout of the belt in response to movement of the vehicle occupant during normal vehicle operation. However, at the onset of a crash, the retractor becomes automatically locked, to restrain further belt payout, and to keep the occupant in her or his seat. Invariably the retractor is not capable of eliminating seat belt slack about the occupant for a number of known factors.
Recently, it has been proposed to design an occupant restraint system with a tensioning device (also referred to as a “belt tightener” or “pretensioner”) and/or a separate load-limiting device, to better control the manner in which force(s) on an occupant are applied during a vehicle collision. Specifically, a tensioning device applies a positive force to the belt immediately at the onset of a collision, to tighten the belt against the occupant. A load-limiting device acts between the belt or retractor and a structural part of the vehicle and absorbs kinetic energy of an occupant in a controlled manner as the occupant loads the restraint during the collision. The load-limiting device can also be incorporated within the tensioning device. When a tensioning device/belt tightener and load-limiting device are combined into an occupant restraint system, the tensioning device reduces residual slack in the seat belt system at the onset of a collision and the load-limiting device absorbs kinetic energy of an occupant in a controlled manner as the occupant loads the restraint during the collision.
U.S. Pat. No. 6,186,549 B1 discloses a known construction for a vehicle seat belt tensioning device. A piston is disposed in a cylinder, and at the onset of a collision is driven in a predetermined direction to tighten the belt about a vehicle occupant. The belt-tensioning device of that patent includes a one-way clutch mechanism. This one-way clutch mechanism includes an array of metal balls that surround a sleeve of the piston of the tensioning device. The annular array of metal balls is carried with the piston when the piston is driven in the predetermined direction. When the piston reaches the end of its stroke in the predetermined direction, and the seat belt has been tightened about the vehicle occupant, force applied by the occupant to the tensioning device will cause the array of metal balls to be immediately driven outward into engagement with the cylinder, thereby virtually instantaneously locking the piston against movement in a return direction. Thus, with this type of belt tensioning device, once the tensioning device has tightened the belt about the vehicle occupant, any subsequent take-up and/or dissipation of force comes from other components of the restraint system (e.g. it may come from an additional load-limiting device incorporated into the restraint system).
The present invention provides a new and useful belt-tensioning device for an occupant restraint, designed to tension a belt about an occupant at the onset of a vehicle collision, and which is also designed to provide a measure of force dissipation as the occupant begins to load the belt during the collision. Thus, the same structure that provides a belt-tensioning function also provides a load-limiting function that absorbs kinetic energy of an occupant in a controlled manner as the occupant loads the restraint during a collision.
In its preferred form, the present invention provides a tensioning member that moves in one direction to tighten a belt about a vehicle occupant, and a braking device configured to apply a controlled braking force to movement of the tensioning member in the opposite direction after the tensioning member has tightened the belt about the vehicle occupant. An array of braking members applies different levels of braking force to movement of the tensioning member in the opposite direction, thereby providing controlled displacement of the tensioning member in the opposite direction as the occupant loads the restraint during a collision.
These and other features of the present invention will become further apparent from the following detailed description and the accompanying drawings.